CVE-2022-49977

In the Linux kernel, the following vulnerability has been resolved:

ftrace: Fix NULL pointer dereference in is_ftrace_trampoline when ftrace is dead

ftrace_startup does not remove ops from ftrace_ops_list when ftrace_startup_enable fails:

register_ftrace_function ftrace_startup __register_ftrace_function … add_ftrace_ops(&ftrace_ops_list, ops) … … ftrace_startup_enable // if ftrace failed to modify, ftrace_disabled is set to 1 … return 0 // ops is in the ftrace_ops_list.

When ftrace_disabled = 1, unregister_ftrace_function simply returns without doing anything: unregister_ftrace_function ftrace_shutdown if (unlikely(ftrace_disabled)) return -ENODEV; // return here, __unregister_ftrace_function is not executed, // as a result, ops is still in the ftrace_ops_list __unregister_ftrace_function …

If ops is dynamically allocated, it will be free later, in this case, is_ftrace_trampoline accesses NULL pointer:

is_ftrace_trampoline ftrace_ops_trampoline do_for_each_ftrace_op(op, ftrace_ops_list) // OOPS! op may be NULL!

Syzkaller reports as follows: [ 1203.506103] BUG: kernel NULL pointer dereference, address: 000000000000010b [ 1203.508039] #PF: supervisor read access in kernel mode [ 1203.508798] #PF: error_code(0x0000) - not-present page [ 1203.509558] PGD 800000011660b067 P4D 800000011660b067 PUD 130fb8067 PMD 0 [ 1203.510560] Oops: 0000 [#1] SMP KASAN PTI [ 1203.511189] CPU: 6 PID: 29532 Comm: syz-executor.2 Tainted: G B W 5.10.0 #8 [ 1203.512324] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [ 1203.513895] RIP: 0010:is_ftrace_trampoline+0x26/0xb0 [ 1203.514644] Code: ff eb d3 90 41 55 41 54 49 89 fc 55 53 e8 f2 00 fd ff 48 8b 1d 3b 35 5d 03 e8 e6 00 fd ff 48 8d bb 90 00 00 00 e8 2a 81 26 00 <48> 8b ab 90 00 00 00 48 85 ed 74 1d e8 c9 00 fd ff 48 8d bb 98 00 [ 1203.518838] RSP: 0018:ffffc900012cf960 EFLAGS: 00010246 [ 1203.520092] RAX: 0000000000000000 RBX: 000000000000007b RCX: ffffffff8a331866 [ 1203.521469] RDX: 0000000000000000 RSI: 0000000000000008 RDI: 000000000000010b [ 1203.522583] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8df18b07 [ 1203.523550] R10: fffffbfff1be3160 R11: 0000000000000001 R12: 0000000000478399 [ 1203.524596] R13: 0000000000000000 R14: ffff888145088000 R15: 0000000000000008 [ 1203.525634] FS: 00007f429f5f4700(0000) GS:ffff8881daf00000(0000) knlGS:0000000000000000 [ 1203.526801] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 1203.527626] CR2: 000000000000010b CR3: 0000000170e1e001 CR4: 00000000003706e0 [ 1203.528611] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 1203.529605] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Therefore, when ftrace_startup_enable fails, we need to rollback registration process and remove ops from ftrace_ops_list.

Weakness

The product dereferences a pointer that it expects to be valid but is NULL.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/4c34a2a6c9927c239dd2e295a03d49b37b618d2c
• https://git.kernel.org/stable/c/8569b4ada1e0b9bfaa125bd0c0967918b6560fa2
• https://git.kernel.org/stable/c/934e49f7d696afdae9f979abe3f308408184e17b
• https://git.kernel.org/stable/c/c3b0f72e805f0801f05fa2aa52011c4bfc694c44
• https://git.kernel.org/stable/c/d81bd6671f45fde4c3ac7fd7733c6e3082ae9d8e
• https://git.kernel.org/stable/c/dbd8c8fc60480e3faa3ae7e27ebe03371ecd1b77
• https://git.kernel.org/stable/c/ddffe882d74ef43a3494f0ab0c24baf076c45f96
• https://git.kernel.org/stable/c/e4ae97295984ff1b9b340ed18ae1b066f36b7835